Method and apparatus for polishing metals



1951 w. HELLING EIAL 2,968,577

METHOD AND APPARATUS FOR POLISHING METALS Filed July 3, 1956 a 5; FIG. 2 H 5 I I I II E 6 iiiliiiZQllQfQQf F 6 .3

INVENTOR.' Werner Helling n y; H 'hrich Net/"11's METHOD AND APPARATUS FOR POLISHING METALS Werner Helling, Grevenhroich, and Heinrich Neunzig, Gindorf, near Grevenbroich, Germany, assignors to Vereinigte Aluminium-Wake Aktiengesellschaft, Bonn, Germany Filed July 3, 1956, Ser. No. 595,792 Claims priority, application Germany July 8, 1955 17 Claims. (Cl. 117-49) The present invention relates to a method and apparatus for polishing metals, and more particularly it relates to a method and apparatus for forming a stable glossy surface on metal bodies, especially on metal bodies consisting of aluminum or aluminum alloys.

Metal bodies of aluminum or aluminum alloys, or bodies of other metals or their alloys are frequently provided with a glossy surface which is made resistant against mechanical and chemical attacks by being covered with a transparent protective layer. The thus-achieved improvement in the appearance of the metallic surface has opened many new uses especially for aluminum.

In the beginning it was attempted to achieve a glossy surface on bodies of aluminum or aluminum alloys by polishing the same in the same manner in which to date still silver, brass, nickel and other metals are polished, namely by dry polishing for instance by means of felt disks or wheels and employing a fat-containing polishing paste. However, the results thus obtained with aluminum surfaces are not satisfactory.

Surface treatment of aluminum by means of chemical and anodic methods, preferably after first treating the aluminum surface by mechanical dry polishing, have resulted in glossy surface appearance which can be ob tained in a relatively economical manner. However, these methods depend on highest purity of the aluminum surface. Already small quantities of impurities such as 0.02% of iron in the aluminum cause considerable diminishing of the gloss that can be obtained by this method. Consequently the use of chemical and anodic methods for obtaining a glossy aluminum surface have greatly favored the use of high purity, refined aluminum and its alloys. It is the great disadvantage of the known chemical and anodic methods for obtaining a high gloss aluminum surface that the result is so greatly dependent on the degree of purity of the metal. It cannot be avoided that the chemical or anodic processes for htaining a glossy aluminum surface cause an attack of varying degree on the metal structure. For this reason any faults in the surface of the aluminum body such as inclusion of oxides or accumulation of metallides become more apparent by such treatment of the aluminum sur face. Consequently, the chemical and anodic treatment of aluminum surfaces does frequently not achieve the desired results especially when the aluminum does not possess a sufficiently high degree of purity. Generally these methods cannot be used for castings. Consequently, there exists a great demand for a generally useful method of obtaining a high glossy surface on aluminum and aluminum alloy bodies which does not depend on the purity of the aluminum.

It is therefore an object of the present invention to overcome the aforementioned disadvantages of existing methods of obtaining a glossy surface.

It is another object of the present invention to pro vide a method and apparatus which permits the forming Patented Jan. l7, lg fil of a glossy surface on metal bodies in a simple and economical manner.

It is yet another object of the present invention to provide a method whereby aluminum bodies of relatively low purity or bodies of aluminum alloys made of an aluminum or relatively low purity can be provided with a glossy surface.

It is yet another object of the present invention to provide a method whereby a stable glossy surface can be obtained on aluminum and aluminum alloys castings.

It is still another object of the present invention to provide a polishing apparatus capable of achieving a high gloss on the surface of metal bodies.

Other objects and advantages of the present invention treating the body with a pickling solution, wet polishing the body, and forming a transparent protective cover layer on the wet-polished body, whereby a stable glossy surface is formed thereon.

In a preferred embodiment, the present invention consists in a method of forming a stable glossy surface on a body of a substance belonging to the group consisting of aluminum and aluminum alloys, comprising in the indicated sequence, the steps of dry polishing the body with a polishing paste, treating the dry-polished body at a temperature of between 40 and 70 with a pickling solution essentially consisting of an aqueous solution of between 5 and 20% by weight of sodium hydroxide, subsequently wet polishing the body with a polishing fluid comprising a supension of particles of hydrate of alumina in a liquid medium, at least 40% of the particles having the size of less than 5 microns and substantially all of the particles having a size of less than microns, while cooling the polishing fluid so as to maintain the same at a predetermined relatively low temperature, the polishing fluid being applied to the surface of the body with a rotating polishing member at least the working surface of which consists essentially of a porous plastic material belonging to the group consisting of natural and synthetic rubbers, viscose, urea resins, phenolic resins, polyurethanes, polystyrenes and polyvinyl chlorides, the rotating polishing member being adapted to apply the polishing fluid to the surface of the body, and forming a transparent protective cover layer on the wet-polished body, whereby a stable glossy surface is formed thereon.

The present invention also contemplates in a polishing apparatus adapted to wet-polish the surface of a metal body, a polishing member having a working surface consisting of a porous plastic material.

Surprisingly, it has now been found that fault-free glossy surfaces can be obtained on aluminum and aluminum alloy bodies, independent of the degree of purity and the structure of the metal, by treating the surface of the aluminum or aluminum alloy body after the dry polishing thereof with a pickling solution, and by subsequently-preferably under cooling--wet--polishing the same, whereafter a transparent cover layer such as may be formed by anodic oxidation, or a lacquer layer is applied.

It has been found that the dry polishing with or without polishing paste causes the formation of a diificultly soluble surface layer which probably consists of partly dehydrated aluminum oxide hydrates such as Boehmite, which layer furthermore is usually contaminated. with rubbed off aluminum particles. This cover layer impairs the quality of the polished surface and is also the cause for a' dulling or clouding of subsequently applied oxide layers such as are formed by an anodizing process. The customary pre-treatment of the aluminum or aluminum alloy surface prior to application of the anodic oxidation layer with degreasing agents does not remove the above described surface layer. Chemical or anodic methods to obtain a glossy surface will strip-otf the layer formed during the dry polishing, however, the above described disadvantages limit the usefulness of such chemical or anodic methods in the case of bodies made of aluminum or aluminum alloys of low purity.

According to the method of the present invention, the surface layer which is formed during the dry polishing is removed by using suitable pickling solutions, and the required smoothing of the surface is completed by a subsequent wet-polishing step in which also any dulling of the surface caused by the pickling step is eliminated. In this manner, the method of the present invention avoids the disadvantages experienced in the anodic or chemical treatment of aluminum and aluminum alloy bodies especially such of relatively low aluminum purity.

As pickling solutions according to the present invention may be used the pickling solutions known in the art for the pickling of aluminum, for instance sodium hydrox ide, and for the wet-polishing, excellent results have been obtained with polishing agents such as particles of hydrated alumina suspended in a liquid medium such as water. Preferably the particles of hydrated alumina have a size of less than 75 microns, and preferably at least 40% of the particles have a size of less than 5 microns. The temperature of the polishing fluid rises during circulation of the same and, in order to maintain the temperature relatively low, in the neighborhood of room temperature it is preferred to cool the polishing fluid.

According to preferred embodiments of the present invention, the polishing fluid also contains substances which will increase the viscosity of the fluid and which will improve its wetting action. For increasing the viscosity of the polishing fluid, mucilage or water soluble cellulose derivatives may be incorporated in the polishing fluid, and as wetting agents small quantities of sulfonates may be added.

Obviously, between the individual steps of the method of the present invention, customary washing and cleansing steps have to be arranged for removal and/ or neutralization of the various treatmentsolutions such as the pickling solution and the polishing fluid.

In this manner it is. possible to obtain on aluminum or aluminum alloy bodies surfaces of outstanding glossiness. The thus-obtained surfaces of high-gloss can then easily be protected by coating the same with a transparent lacquer or by forming an anodic oxide layer thereon. The excellent results obtained according to the present invention by forming an anodic oxide layer on the wetpolished surface should be emphasized.

When glossy surfaces are to be formed on aluminum or aluminum alloy bodies which have been pre-treated by rolling operations or the like, i.e., when glossy surfaces are to be formed on foils, bands, sheets, wires or profiles obtained by rolling or extrusion processes, that is on bodies which already have been exposed to the equivalent of dry polishing during the preceding manufacturing steps, or when a glossy surface is to be obtained on a casting, the surface of which has already been smoothened during the casting process such as frequently is the case with articles obtained by chill casting, it is not necessary to dry polish the aluminum or aluminum alloy body. In such cases where the surface of the aluminum or aluminum alloy body has already received a pre-treatment corresponding to the dry-polishing thereof, the above described first step of the method of the present invention which consists in a dry polishing of the aluminum or aluminum alloy body may be omitted.

- In such case the aluminum or aluminum alloy bodies which already possess a relatively smooth surface are treated with a pickling solution in a manner known in the art, for instance preferably in an alkaline pickling solution, and are subsequently polished with a suspension of suitable solid polishing particles in a liqiud medium. After the wet-polishing, and after the customary washing of the wet-polished workpiece, the same is then provided with a transparent protective cover layer in known mannor for instance with an anodically produced oxide layer, or with a lacquer coating.

it is a special advantage of the method of the present invention that by making unnecessary the step of dry-polishing bodies which by some other means have obtained a relative smooth aluminum or aluminum alloy surface, it is now also possible to obtain a high gloss on surfaces which due to their configuration can only diflicultly or not at all be dry-polished. Furthermore, to omit in such cases the step of dry-polishing results in a simplification of the entire proecss.

Thus it is possible to continuously treat aluminum or aluminum alloy bodies which can be woundabout a core or the like, such as foils, bands, wires, etc. In this case, the aluminum body is pickled, wet-polished and subsequently provided with a suitable transparent protective layer in one continuous process, for instance on a conveyor belt line. Between the individual steps of the method such as the pickling, Wet-polishing and anodizing. or coating, the necessary washing and cleaning baths are arranged so that the foil, wire or the like passes through such washing or cleaning bath between successive processsteps.

According to a preferred embodiment of the present invention, the time required for the wet-polishing of sheets, bands or profiles obtained in a rolling mill operation and the like can be shortened by smoothing the sur-- face of these aluminum or aluminum alloy bodies prior to the wet-polishing of the same by rolling between polished steel rollers.

It is also within the scope of the present invention to improve the wet-polishing step which is executed with a polishing fluid comprising a suspension of solid particles in the liquid medium, whereby the liquid medium may also be a liquid other than water.

Customarily wet-polishing operations are executed with polishing wheels, the working surfaces of which are covered with cloth or felt, or with polishing wheels which in their entirety consist of cloth or felt (so-called flexible buffing wheel). Furthermore, textile bands are also used for this purpose. By employing any of the aforementioned polishing members it is not possible to achieve an especially high gloss, to the contrary there always remain microscopically fine scratches, which for instance give to such polished metal surface an undesirable cloudy luster. It is a further disadvantage of the above-discussed devices that the textile materials absorb and retain only small quantities of the polishing fluid. Consequently, textile covered polishing wheels cause spinning off of considerable quantities of the polishing fluid due to the centrifugal forces created by the rotating polishing wheel. The spun-off polishing fluid circulates without useful effect.

Surprisingly, it has now been found that a considerable increase in the quality of the polish and gloss of aluminum and aluminum alloy surfaces as well as of other metal and metal alloy surfaces can be obtained by employing instead of textile polishing wheels, polishing wheels or bands which have at least a working surface made of porous plastic materials. Elastomers such as natural or synthetic rubber, viscose, urea or phenolic resins, polyurethanes, polystyrenes, polyvinyl chlorides and others may be employed. The polishing wheels or bands or other polishing members may be formed completely of such porous plastic materials or may be entirely or in part covered with thesame. Preferably, materials having open pores of a size between and 1,000 microns are used.

A further advantage of employing such porous elastomers consists in the reduction of the required speed of the wheels or hands as compared with the speed required when using the customary felt or cloth polishing members. Consequently the centrifugal forces are less, the polishing liquid is absorbed into the pores of the polishing member and retained therein without being spun off in large quantities due to excessive centrifugal forces.

The disk or wheels made of such synthetic or natural elastomers, or at least having working surfaces covered with the same absorb the polishing fluid and retain a large portion of the same, since the centrifugal forces, due to the slow surface speed do not cause any spinningofl of polishing fluid. It is a further advantage of the polishing members according to the present invention that the metal or metal alloy body which is to be polished can be strongly pressed onto the working surface of the disk which can be formed of commensurate width. Thereby the metal body will partially be embedded into the surface of the plastic porous disk under temporary deformation of the disk. In this manner it is possible also to polish metal bodies which have an uneven surface such as reliefs or portions of mountings, instruments and the like, since the polishing disk acts on a larger portion of the surface of the metal body. Thereby too, the polishing fluid is for all practical purposes retained in the porous plastic wheel and is not spun-off.

The surface speed or rim speed of polishing wheels or hands made of porous elastomers can be as low as between 2 and 3 meters per second. At such low speed many of the dangers which otherwise exist when polishing uneven bodies are avoided. Customary polishing disks having textile covered working surfaces or polishing bands of customary textile material have to be operated with considerably higher speeds such as speeds of between 20 and 30 meters per second since otherwise the polishing effect can not be obtained. The danger, as is well known, consists in the possibility that the metal body may attach itself to the fast moving polishing member and may then be thrown off the same. Consequently the low speed porous plastic polishing wheels or bands according to the present invention are especially suitable for polishing metal bodies of complicated uneven configuration. Accordingly the previously existing difliculties in the Wet-polishing of metal bodies with suspensions of solid particles in a liquid medium can be avoided by employing the polishing members of the present invention which have at least working surfaces made of porous natural or synthetic elastomers.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

Fig. 1 is a schematic elevational view of an embodiment of the apparatus of the present invention;

Fig. 2 is a schematic elevational view of another embodiment of an apparatus according to the present invention; and

Fig. 3 is still another schematic elevational view of a different embodiment of the present invention.

Referring now to the drawing and particularly to Fig. 1, a motor 1 is shown driving a shaft 2. On shaft 2 is mounted a polishing wheel 3 having an outer working portion 4, the working surface of which will come in contact with the metal body to be polished. Working portions 4 of polishing member 3 is made of a porous plastic material adapted to apply a polishing fluid to the metal body. Polishing fluid squeezed out of the porous plastic working portion of polishing member 3 is collected in a vessel 5 and pumped by pump 6 through conduit 7, from the open end of which the polishing fluid is again introduced to the porous plastic working portion 4 of polishing member 3. The polishing fluid, while passing through conduit 7 is cooled by cooling means 8.

The different embodiment shown in Fig. 2 includes a hollow shaft 11 on which is mounted a polishing wheel 12 which is made entirely of a porous plastic material. Brackets 13 are provided for giving additional support to polishing member or wheel 12. Polishing fluid is pumped through conduit 14 into hollow shaft 11 and enters the porous plastic polishing wheel 12 through hollow shaft 11. Polishing fluid squeezed off the working surface of polishing wheel 12 when the same is in contact with a metal body to be polished, is collected in vessel 5 from where it flows to pump 6 for being recirculated through conduit 14. Cooling means 8 are provided for controlling the temperature of the polishing fluid.

The embodiment shown in Fig. 3 differs from the embodiment shown in Fig. 1 by having a polishing band 21 provided with a working portion 22 formed of a porous plastic material.

The operation of the apparatus of the present invention may for instance be as follows:

A disk made of finely porous polyurethane, having a Width of about mm. and a diameter of about 300 mm. is mounted on a grinding head in a manner similar to the mounting of a grinding wheel. The pores of the polyurethane wheel preferably have a size of between 100 and 1,000 microns. The polyurethane polishing Wheel is mounted on a shaft by means of two lateral brackets preferably made of wood, hard rubber or a suitable strong synthetic material and having rounded edges. The polishing wheel is rotated with about turns per minute corresponding to a peripheral velocity of about 2.5 meters per second. The wheel is completely saturated with polishing fluid consisting for instance of a suspension of aluminum oxide hydrate or alumina in water to which a small quantity of a commercial wetting agent has been added. The metal bodies to be polished are firmly pressed against the polishing wheel so that they penetrate to some extent into the resilient working surface thereof. Thereby polishing fluid is pressed out of the polishing wheel and due to the low velocity remains for a short period of time on the surface of the metal body from which the fluid slowly drops into a collecting vessel. It should be noted that due to the low velocity and correspondingly small centrifugal force, the polishing fluid is not spun-off the polishing Wheel. Consequently it is not necessary to provide bufler sheets or other protective devices to catch polishing fluid spraying off the apparatus. The polishing fluid dropping from the metal body is collected and returned to the polishing wheel as indicated in the description of the drawing. The porous plastic materials of which the entire polishing Wheel may be formed are also well suited for conducting the polishing fluid to the working surface of the polishing wheel, for instance by providing a hollow shaft on which the polishing Wheel is mounted and through which the polishing fluid is supplied. This has been illustrated in Fig. 2. The polishing fluid may also be pressed into the small intervening space between several polishing wheels which are mounted next to each other. In this manner, too, the polishing fluid can be supplied to the working surface of the polishing Wheel.

In the following Table I, several different forms of executing the method of the present invention are compared with the methods of the prior art. The results indicated in Table I, clearly show the increase in total and specular reflectivity which can be obtained under otherwise equal conditions by following the method of the present invention.

The examples which are summarized in Table I are given as illustrative only, the present invention however not being limited to the specific details of the examples.

The individual steps of the method are indicated in the following table by capital letters.

A. DRY POLISHING A polishing paste consisting of 66mm of finely subdivided alumina, 26 parts of stearin, 6 parts montan wax, and 2 parts of petroleum jelly was used to dry polish a metal body with a flexible polishing wheel made of nettle cloth and having a diameter of 300 millimeters and a width of 40 millimeters. The dry polishing was executed at a circumferential speed of 50 meters per second for a period of 2 minutes.

meters per second. The above-described polishing fluid was sprayed onto the polishing wheel. Wet polishing was carried out for a period of 10 minutes. Thereafter the metal bodies were sprayed with water.

D. WET POLISHING WITH POROUS PLASTIC POLISHING WHEEL The polishing fluid used was identical to the one described under C above. Thepolishing wheel was made of finely porous polyurethane (Moltopren 0.055 blue, thickness 10 centimeters). The wheel had a diameter of 300 millimeters and a width of 100 millimeters and was mounted on a grinding head in a similar manner as a grinding wheel. The wheel was rotated with 160 revolutions per minute, corresponding to a circumferential speed of about 2.5 meters per second. The wheel was completely saturated with polishing fluid, the polishing fluid which dropped off the wheel and/ or the metal body was caught and recirculated to the polishing wheel. Polishing was carried out for 4 minutes.

After completion of the wet polishing, the metal bodies were cleaned by spraying with water.

E. ANODIC OXIDATION B. PICKLING The aluminum or aluminum alloy metal bodies were The metal bodies were treated with a Sodium anodically oxidized for 10 minutes in 20% aqueous sulhydroxide-containing pickling solution. In experiments furlc acld at f a Current densrty of 1 5 amperes 1, 4, 5, 8, 9, 11, 12 14 and 16 the metal bodies were per 100 square centimeters. The thus obtained oxide immersed for Seconds in 10% aqueous sodium layer had a thickness of approximately 5 microns. droxide solution having a temperature of 55 C., sub- 30 F. LACQUER COATING sequently rinsed with water and then neutralized by being immersed for a short period of time in 20% aqueous The Wet pqhshed.metal bodles dlstlued water, then dipped in ethanol and dried in an air stream nitric acid at room temperature. a

In Ex eriment 3 the icklin treatment was conducted havmg a temperature of 50 Thereafter the metal P p g bodies were immersed in Zapon lacquer and suspended in as described above, however, the metal bodies were lIIlair for drying gif gi i gi i z g qi :g 28F 2 of The examples described in the following tables were 1 y 1 g p carried out as indicated above. However, similar or C. WET POLISHING WITH TEXTILE POLISHING substantially similar results can also be obtained by car- WHEEL 4.) rying out the individual steps in different manners. Sev- The polishing fluid for the wet polishing of metal bodies g i i g Whlch F?? employed arefiwnkied was prepared by diluting 300 cubic centimeters of a figzg Wlt owever mung the present Invention commercial suspension of polishing alumina with 1 liter of water and adding thereto 1.3 grams of an oxyethyl- 4 DRY POLISHING methyl cellulose of medium viscosity (Tylose SL 400). 5 Depending on the condition of the surface of the metal A flexible polishing wheel consisting of several layers body it is sometimes desirabie to precede the dry polishof absorbent soft cotton which were sewn together, was ing with a pre-grinding with a stearin-containing paste in used. The diameter of the polishing wheel was 300 milwhich emery of particle size 6/0 is distributed. limeters and the Width 40 millimeters. The cir'cum- Instead of the polishing paste used in the experiments ferential speed of the rotating polishing wheel was 20 one may for instance also use a polishing paste which Table I E Metal Body Reflection X. No. Method of Treatment Composition Surface Condition and Shape S ecular, Total,

Percent Percent 1--.- Al-Mg allov including 0.01% Cu, 0.011% Normal commercial sheet with cold rolled A; B (10% NaOH, 0., 30 sec.); 70.3 82.4

Zn, 0.000% Si, 0.033% Fe, 0.002% Mn, finished surface. 0; E. 1.92% Mg, balance Al. 2---- d0 ;0 63.0 81.0 3---- do A;EB(20% NaOH,20 0.,5minutes); 21.7 74.8

4.... mac d0 A;l(10%NaOH,55O.,30see.);E 28.9 1 63.2 5 Aluminum: 90.8% Al, 0.12% Si, 0.07% Gold rolled sheet with s ecially well rolled B (10% NaOH, 55 0.,30 sec.); 0; E. 70.3 80.2

Fe, 0.02% Cu, traces Zn. surface (rolled. with polished steel rollers). 6 do d E 22.1 40.0 7 Aluminum alloy containing 99% of high A; E 41.2 81.2

purity aluminum (purity 99.99%) and Same as 4 22. 7 63. 8 BA(10}E% NaOH, 55 0., 1 minute); 40.2 79.2 A; (3;1'3 62.8 82.0 Same as 1 77; 3 80:1 NaOH, 55 0., 30 sec.); 79.6 89.9 74.2 86.0 do 81.4 86.9 15 Al-Mg alloy including 0.12% Si, 0.035% Same as 7 43. 0 77.0

Fe, 2.1% Mg, balance Al. handle). 16... do Same as 12 81.0 88. 2

B. PICKLING The following may serve as an example of an acidic pickling solution: 4 parts by volume of 54% nitric acid and 1 part by volume of 70% hydrofluoric acid. Treatment with this acidic pickling solution to be continued for 60 seconds at room temperature and to be followed by rinsing in flowing water.

C. WET POLISHING WITH TEXTILE POLISHING WHEEL As wet polishing fluid can also be used for instance a liquid consisting of: 1 part by volume of Menzerna- Polishing Emulsion V, 2 parts by volume water, with an addition of grams of Tylose SL 400 (oxymethylethyl cellulose) per liter of the above mixture.

E. WET POLISHING WITH POLISHING MEMBER HAVING A POROUS PLASTIC WORKING POR- TION.

The following materials may be advantageously used for the working portion of polishing Wheels, polishing bands or other polishing members: foam material made of viscose, foam material made of polystyrene, foam material made under the trade name Poramol. While it is preferred to use porous plastic materials having pores the size of which is between 100 and 1000 microns, good results have also been obtained with the above-mentioned three foam materials when the size of the pores was increased up to 1.5 millimeters.

By evaluating the various method steps with respect to the reflection values obtained thereby, it can be seen that aluminum sheets containing 99.8% aluminum and which have been anodically oxidized in cold rolled condition (Example 6), show a specular reflection of only 22.1% and a total reflection of only 40.0%.

The reflection values increase if the aluminum workpiece is anodically oxidized in dry polished condition. In this case it was found according to Example 2 that normal commercial sheets of aluminum magnesium alloy will show a specular reflection of 63.0% and a total reflection of 81.0%. According to Example 7 sheets of an aluminum magnesium alloy made with high purity aluminum will, under such conditions, show a specular reflection of 41.2% and a total reflection of 81.2%. Similarly treated workpieces of aluminum magnesium alloy obtained by chill casting (Example show a specular reflection of 43.0% and a total reflection of 77.0%.

When the dry polished workpieces are pickled either with cold concentrated sodium hydroxide solution or with warm diluted sodium hydroxide solution, and subsequently anodically oxidized, reflection values drop in the case of commercial aluminum magnesium alloy sheets (Example 3) to a specular reflection of 21.7% and a total reflection of 74.8%, and according to Example 4, to a specular reflection of 28.9% and a total reflection of 63.2%.

Aluminum sheets which after pickling were dry polished and anodically oxidized (Example 9) show in comparison with dry polished, pickled and anodically oxidized sheets (Examples 3 and 4) an increase in reflection values to approximately the same values as were obtained with dry polished sheets which were anodically oxidized without pickling (Examples 7 and 15). According to Example 2 a specular reflection of 40.2% and a total reflection of 79.2% are obtained with aluminum magnesiurn alloy sheets made of high purity aluminum which are first pickled, then dry polished and subsequently anodically oxidized.

By proceeding according to the method of the present invention, i.e., dry polishing, pickling, wet polishing with a textile polishing wheel and subsequently anodically oxidizing as per Examples 1 and 11, a further increase in the values of especially the specular reflection is clearly apparent. The thus-obtained values, however, are further exceeded by those which are obtained when the textile polishing wheel used in wet polishing is replaced by a wheel made of porous plastic material (Examples 12, 14 and 16). These results are summarized in the following Table II.

Table II Reflection Ex. Method of Treatment Composition N0. Soec- Total,

ular, Per- Percent cent 1 Dry polishing, piclr- Commercial alumi- 70. 3 82. 4

ling, wet polishing num magnesium with textile wheel alloy sheet. anodieall y oxidizing. 11 Same as 1 Aluminum magne- 77. 3 80.1

sium alloy with high purity aluminum. 12...- Dry polishing, pick- Commercial alumi- 79. 6 89. 9

ling, wet polishing num magnesium with porous plastic alloy sheet. wheel, anodically oxidizing. 14...- Same as 12 Aluminum magne- 81. 4 86. 9

sium alloy with high purity aluminum. 16.... do Aluminum mague- 81.0 88.2

sium alloy chill casting.

Sheets which were first dry polished, then wet polished and subsequently anodically oxidized (Examples 10 and 13) show an increase in reflection values when the wet polishing is accomplished with porous plastic polishing members (Example 13). This comparison clearly shows the further improvement obtained by wet polishing with porous plastic polishing members.

The examples clearly show that surfaces of superior reflectivity are obtained according to the present invention on aluminum and aluminum alloys when the same are pickeld after being dry polished, subsequently wet polished, and finally anodically oxidized. A further improvement is achieved when for the wet polishing polishing wheels or the like are employed which have at least working portions made of porous plastic materials such as are described further above.

The improvement obtained by using the porous plastic polishing members of the present invention is, however, not limited to aluminum and aluminum alloy surfaces. Substantial improvements are achieved on metal and metal alloy surfaces other than aluminum and aluminum alloys.

In the following Table III, reflection values obtained by wet polishing brass sheets with conventional textile Table III Metal Body Reflection Ex. N0.

Method of Surface Treatment Condition and Shape Soec ular, Percent Total, Percent Composition 17-.. Cold rolled A: dry polished;

C: wet polished with textile polishing wheel.

A: dry polished;

D: Wet oolished with porous lastic polishing wheel.

A: dry polished;

0: wet polished with textile polishing wheel; 1*: lacquered.

A: dry polished;

D: wet polished with porous plastic polishing wheel; F: lacquered.

Commercial 69 7 8 brass sheets.

do .do

19-.. v do .do 54 66 20-.- do .do 73 polishing wheels and porous plastic polishing wheels are compared.

It is apparent from the results indicated in Table III that higher reflection values are obtained by wet polishing with an elastic, porous, plastic polishing member according to the present invention, as compared with using conventional textile or the like polishing members.

According to Examples 19 and 20, the wet polished brass sheet surface was lacquered with a colorless Zapon lacquer which caused an expected drop in reflection values, irrespective of whether the sheets had been Wet polished with porous plastic or textile polishing members.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended Within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a method of forming a glossy surface on a smooth body of a substance belonging to the group consisting of aluminum and aluminum alloys, in the indicated sequence, the steps of treating said body with a pickling solution to remove surface oxide; and wet mechanically polishing said body while the same is substantially free of said surface oxide, whereby a glossy surface is formed thereon.

2. In a method of forming a glossy surface on a body of a substance belonging to the group consisting of aluminum and aluminum alloys, in the indicated sequence, the steps of dry polishing said body; treating said dry-polished body with a pickling solution to remove surface oxide; and wet mechanically polishing said body while the same is substantially free of said surface oxide, whereby a glossy surface is formed thereon.

3. A method of forming a stable glossy surface on a body of a substance belonging to the group consisting of aluminum and aluminum alloys, comprising in the indicated sequence, the steps of dry polishing said body; treating said dry-polished body with a pickling solution to remove surface oxide; subsequently wet mechanically polishing said body While the same is substantially free of said surface oxide; and forming a transparent protective cover layer on said wet-polished body, whereby a stable glossy surface is formed thereon.

4. A method of forming a stable glossy surface on a body of a substance belonging to the group consisting of aluminum and aluminum alloys, comprising in the indicated sequence, the steps of dry polishing said body with a polishing paste; treating said dry-polished body with an alkaline pickling solution to remove surface oxide; subsequently wet mechanically polishing said body while the same is substantially free of said surface oxide; and forming a transparent protective cover layer on said wet-polished body, whereby a stable glossy surface is formed thereon.

5. In a method of forming a glossy surface on a body of a substance belonging to the group consisting of aluminum and aluminum alloys, in the indicated sequence, the steps of treating said body with a pickling solution to remove surface oxide; and mechanically Wet polishing said body while the same is substantially free of said surface oxide with a polishing fluid comprising a suspension of solid particles in a liquid medium, said polishing fluid being applied to the surface of said body with a continuously moving carrier member at least the working surface of which consists essentially of a soft resilient porous plastic material adapted to apply said polishing fluid to said surface of said body.

6. In a method of forming a glossy surface on a body 'of a'substance belonging to thegroup consisting of aluminum and aluminum alloys, in the indicated sequence, the steps of treating said body with a pickling solution to remove surface oxide; and mechanically wet polishing said body while the same is substantially free of said surface oxide with a polishing fluid comprising a suspension of solid particles in a liquid medium, said polishing fluid being applied to the surface of said body with a continuously moving carrier member at least the working surface of which consists essentially of a soft resilient porous plastic material belonging to the group consisting of natural and synthetic rubbers, viscose, urea resins, phenolic resins, polyurethanes, polystyrenes and-polyvinyl chlorides, said polishing member being adapted to apply said polishing fluid to said surface of said body.

7. A method of forming a stable glossy surface on a body of a substance belonging to the group consisting of aluminum and aluminum alloys, comprising in the indicated sequence, the steps of dry polishing said body; treating said dry-polished body at a temperature of between about 40 and 70 C. with a pickling solution essentially consisting of an aqueous solution of between about 5 and 20% by weight of sodium hydroxide to remove surface oxide; subsequently wet mechanically polishing said body while the same is substantially free of said surface oxide; and forming a transparent protective cover layer on said wet-polished body, whereby a stable glossy surface is formed thereon.

8. A method of forming a stable glossy surface on a body of a substance belonging to the group consisting of aluminum and aluminum alloys, comprising in the indicated sequence, the steps of dry polishing said body; treating said dry-polished body with a pickling solution to remove surface oxide; subsequently wet mechanically polishing said body with a polishing fluid comprising a suspension of solid polishing particles in a liquid medium, while cooling said polishing fluid while the same is substantially free of said surface oxide; and forming a transparent protective cover layer on said wet-polished body, whereby a stable glossy surface is formed thereon.

9. A method of forming a stable glossy surface on a body of a substance belonging to the group consisting of aluminum and aluminum alloys, comprising in the indicated sequence, the steps of dry polishing said body; treating said dry-polished body with a pickling solution to remove surface oxide; subsequently Wet mechanically polishing said body with a polishing fluid comprising a suspension of particles of hydrate of alumina in a liquid medium while the same is substantially free of vsaid surface oxide; and forming a transparent protective cover layer on said wet-polished body, whereby a stable glossy surface is formed thereon.

10. A method of forming a stable glossy surface on a body of a substance belonging to the group consisting of aluminum and aluminum alloys, comprising in the indicated sequence, the steps of dry polishing said body; treating said dry-polished body with .a pickling solution to remove surface oxide; subsequently wet mechanically polishing said body while the same is substantially free of said surface oxide with a polishing fluid comprising a suspension of particles of hydrate of alumina in a liquid medium, at least 40% of said particles having a size of less than 5 microns and substantially all of said particles having a size of less than 75 microns; and forming a transparent protective cover layer on said wet-polished body, whereby a stable glossy surface is formed thereon.

11. A method of forming a stable glossy surface on a body of a substance belonging to the group consisting'of aluminum and aluminum alloys, comprising in the indicated sequence, the steps of dry polishing said body; treating said dry-polished body with a pickling solution to remove surface oxide; subsequently wet mechanically polishing said body while the same is substantially free of surface oxide with a polishing fluid comprising a suspension of solid polishing particles in a liquid medium and a substance adapted to increase the viscosity of said polishing fluid; and forming a transparent protective cover layer on said Wet-polished body, whereby a stable glossy surface is formed thereon.

12. A method of forming a stable glossy surface on a body of a substance belonging to the group consisting of aluminum and aluminum alloys, comprising in the indicated sequence, the steps of dry polishing said body; treating said dry-polished body with a pickling solution to remove surface oxide; subsequently wet mechanically polishing said body while the same is substantially free of surface oxide with a polishing fluid comprising a suspension of solid polishing particles in a liquid medium and a wetting agent; and forming a transparent protective cover lawer on said wet-polished body, whereby a stable glossy surface is formed thereon.

13. A method of forming a stable glossy surface on a body of a substance belonging to the group consisting of aluminum and aluminum alloys, comprising in the indicated sequence, the steps of dry polishing said body; treating said dry-polished body with a pickling solution to remove surface oxide; subsequently Wet mechanically polishing said body while the same is substantially free of surface oxide with a polishing fluid comprising a suspension of solid polishing particles in a liquid medium, said polishing fluid being applied to the surface of said body with a rotating carrier member at least the working surface of which consists essentially of a soft resilient porous plastic material adapted to apply said polishing fluid to the surface of said body, said working surface of said carrier member rotating at a peripheral speed of about 2.5 meters per second; and forming a transparent protective cover layer on said wet-polished body, whereby a stable glossy surface is formed thereon.

14. A method of forming a stable glossy surface on a body of a substance belonging to the group consisting of aluminum and aluminum alloys, comprising in the indicated sequence, the steps of dry polishing said body; treating said dry-polished body with a pickling solution to remove surface oxide; subsequently wet mechanically polishing said body while the same is substantially free of surface oxide with a polishing fluid comprising a suspension of solid polishing particles in a liquid medium, said polishing fluid being applied to the surface of said body with a rotating carrier member at least the working surface of which consists essentially of a soft resilient porous plastic material belonging to the group consisting of natural and synthetic rubbers, viscose, urea resins, phenolic resins, polyurethanes, polystyrenes and polyvinyl chlorides, said rotating wheel being adapted to apply said polishing fluid to the surface of said body; and forming a transparent protective cover layer on said wet-polished body, whereby a stable glossy surface is formed thereon.

15. A method of forming a stable glossy surface on a body of a substance belonging to the group consisting of aluminum and aluminum alloys, comprising in the indicated sequence, the steps of dry polishing said body; treating said dry-polished body with a pickling solution to remove surface oxide; subsequently wet mechanically polishing said body while the same is substantially free of said surface oxide; and anodizing said thus wet polished body thereby forming a transparent protective oxide layer thereon, whereby a stable glossy surface is formed thereon.

16. A method of forming a stable glossy surface on a body of a substance belonging to the group consisting of aluminum and aluminum alloys, comprising in the indicated sequence, the steps of dry polishing said body; treating said dry-polished body with a pickling solution to remove surface oxide; subsequently wet mechanically polishing said body while the same is substantially free of said surface oxide, and forming a transparent protective lacquer layer on said thus Wet-polished body, whereby a stable glossy surface is formed thereon.

17. A method of forming a stable glossy surface on a body of a substance belonging to the group consisting of aluminum and aluminum alloys, comprising in the indicated sequence, the steps of dry polishing said body with a polishing paste; treating said dry-polished body at a temperature of betwen 40 and with a pickling so lution essentially consisting of an aqueous solution of between 5 and 20% by Weight of sodium hydroxide to remove surface oxide; subsequently wet mechanically polishing said body while the same is substantially free of said surface oxide with a polishing fluid comprising a suspension of particles of hydrate of alumina in a liquid medium, at least 40% of said particles having a size of less than 5 microns and substantially all of said particles having a size of less than microns, while cooling said polishing fluid so as to maintain the same at a predetermined relatively low temperature, said polishing fluid being applied to the surface of said body with a rotating carrier member at least the working surface of which consists essentially of a soft resilient porous plastic material belonging to the group consisting of natural and synthetic rubbers, viscose, urea resins, phenolic resins, polyurethanes, polystyrenes and polyvinyl chlorides, said rotating polishing member being adapted to apply said polishing fluid to the surface of said body; and forming a transparent protective cover layer on said wet-polished body, whereby a stable glossy surface is formed thereon.

References Cited in the file of this patent UNITED STATES PATENTS 2,040,618 Mason et al. May 12, 1936 2,096,309 Pullen Oct. 19, 1937 2,108,603 Mason Feb. 15, 1938 2,222,562 German Nov. 19, 1940 2,630,658 Golightly Mar. 10, 1953 2,650,901 Van der Horst Sept. 1, 1953 2,663,127 Hunt Dec. 22, 1953 2,666,023 Schaaber Jan. 12, 1954 2,683,113 Prance et al. July 6, 1954 2,739,429 Peterson Mar. 27, 1956 2,764,856 Steen et al. Oct. 2, 1956 OTHER REFERENCES Zeerleder: Technology of Aluminum, published in 1936 in Amsterdam, by Nordemann Publishing Co.; pages 226-230, and 234-238. 

1. IN A METHOD OF FORMING A GLOSSY SURFACE ON A SMOOTH BODY OF A SUBSTANCE BELONGING TO THE GROUP CONSISTING OF ALUMINUM AND ALUMINUM ALLOYS, IN THE INDICATED SEQUENCE, THE STEPS OF TREATING SAID BODY WITH A PICKLING SOLUTION TO REMOVE SURFACE OXIDE; AND WET MECHANICALLY POLISHING SAID BODY WHILE THE SAME IS SUBSTANTIALLY FREE OF SAID SURFACE OXIDE, WHEREBY A GLOSSY SURFACE IS FORMED THEREON. 